Canvas in prefab editing scene won't scale its aspect ratio with Game View's in prefab mode.

Hi all, what I wanted is to edit UI prefabs while being able to review its responsive result by scaling Game View's size. But resizing the Game View only makes the UI elements bigger without resizing the canvas they sit on. My guess is resizing Game View affects the pixel numbers of the resolution but not the aspect ratio.

UI prefab mode's canvas does not resize its aspect ratio when I resize the Game View. Incorrect result:
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Further widened Game View and the aspect ratio of Canvas remains unchanged. Incorrect result:
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However, if I re-open the prefab the canvas resized itself correctly upon opening. Correct result:
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Unity version: 2018.4.1f1